The present disclosure relates to systems and methods for percutaneous implantation of a heart valve prosthesis. More particular, it relates to delivery systems and methods for transcatheter implantation of a self-expanding, stented prosthetic heart valve.
Diseased or otherwise deficient heart valves can be repaired or replaced with an implanted prosthetic heart valve. Conventionally, heart valve replacement surgery is an open-heart procedure conducted under general anesthesia, during which the heart is stopped and blood flow is controlled by a heart-lung bypass machine. Traditional open surgery inflicts significant patient trauma and discomfort, and exposes the patient to a number of potential risks, such as infection, stroke, renal failure, and adverse effects associated with the use of the heart-lung bypass machine, for example.
Due to the drawbacks of open-heart surgical procedures, there has been an increased interest in minimally invasive and percutaneous replacement of cardiac valves. With these percutaneous transcatheter (or transluminal) techniques, a valve prosthesis is compacted for delivery in a catheter and then advanced, for example, through an opening in the femoral artery and through the descending aorta to the heart, where the prosthesis is then deployed in the annulus of the valve to be repaired (e.g., the aortic valve annulus). Although transcatheter techniques have attained widespread acceptance with respect to the delivery of conventional stents to restore vessel patency, only mixed results have been realized with percutaneous delivery of a relatively more complex prosthetic heart valve.
Various types and configurations of prosthetic heart valves are available, and continue to be refined. The actual shape and configuration of any particular prosthetic heart valve is dependent to some extent upon native shape and size of the valve being repaired (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, prosthetic heart valve designs attempt to replicate the functions of the valve being replaced and thus will include valve leaflet-like structures. With a bioprosthesis construction, the replacement valve may include a valved vein segment that is mounted in some manner within an expandable stent frame to make a valved stent (or “stented prosthetic heart valve”). For many percutaneous delivery and implantation systems, the self-expanding valved stent is crimped down to a desired size and held in that compressed state within an outer sheath, for example. Retracting the sheath from the valved stent allows the stent to self-expand to a larger diameter, such as when the valved stent is in a desired position within a patient. In other percutaneous implantation systems, the valved stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed on a balloon portion of catheter until it is as close to the diameter of the catheter as possible. Once delivered to the implantation site, the balloon is inflated to deploy the so-configured prosthesis. With either of these types of percutaneous stent delivery systems, conventional sewing of the prosthetic heart valve to the patient's native tissue is typically not necessary.
It is imperative that the stented prosthetic heart valve be accurately located relative to the native annulus immediately prior to full deployment from the catheter as successful implantation requires the transcatheter prosthetic heart valve intimately lodge and seal against the native annulus. If the prosthesis is incorrectly positioned relative to the native annulus, serious complications can result as the deployed device can leak and may even dislodge from the implantation site. As a point of reference, this same concern does not arise in the context of other vascular stents; with these procedures, if the target site is “missed,” another stent is simply deployed to “make-up” the difference.
While imaging technology can be employed as part of the implantation procedure to assist a clinician in better evaluating a location of the transcatheter prosthetic heart valve immediately prior to full deployment, in many instances this evaluation alone is insufficient. Instead, clinicians desire the ability to partially deploy the prosthesis, evaluate a position relative to the native annulus, and reposition the prosthesis prior to full deployment if deemed necessary. Repositioning, in turn, requires the prosthesis first be re-compressed and re-located back within the outer delivery sheath. Stated otherwise, the partially deployed, stented prosthetic heart valve must be “recaptured” by the delivery system, and in particular within the outer sheath. While, in theory, the recapturing of a partially deployed stented prosthetic heart valve is straight forward, in actual practice, the constraints presented by the implantation access path and the stented prosthetic heart valve itself render the procedure exceedingly difficult.
For example, the stented prosthetic heart valve is purposefully design to rigidly resist collapsing forces once deployed. With a self-expanding stented prosthetic heart valve, then, the stent frame must generate a high radial force when expanding from the compressed state to properly anchor itself in the anatomy of the heart. The corresponding delivery sheath segment (or capsule) compressively retaining the stented valve during delivery to the implantation site is radially stiffened to sufficiently resist radial expansion, and conventionally encompasses or surrounds an entire length of the prosthesis (i.e., while the relatively rigid capsule can be proximally coupled to a more compliant catheter shaft, the capsule itself surrounds an entirety of the prosthesis). Further, to facilitate compressed loading of the self-expanding stent frame into the outer sheath, the capsule typically has an increased inner (and outer) diameter as compared to the other, more proximal segments of the outer sheath. As part of most transcatheter heart valve replacement procedures, the delivery system (e.g., a prosthetic heart valve compressively retained within an outer sheath) must traverse the aortic arch (e.g., in a retrograde approach). While the relatively rigid, relatively large delivery sheath capsules are viable for accessing the native heart valve via the aortic arch (or other tortuous vasculature), the so-configured delivery sheath may undesirably buckle or “kink”, especially when traversing the various curvatures of the aortic arch. Once kinked, it is virtually impossible for the delivery sheath capsule to be advanced over a partially-deployed prosthesis as is otherwise necessary for recapture. Simply stated, due to the relatively long stiff section of the conventional delivery sheath, successful delivery of a prosthetic heart valve through the tortuous vasculature, such as required for retrograde delivery of a prosthetic aortic heart valve, as well as recapturing a partially deployed prosthetic heart valve, has proven to be difficult.
In light of the above, although there have been advances in percutaneous valve replacement techniques and devices, there is a continued desire to provide different delivery systems for delivering cardiac replacement valves, and in particular self-expanding stented prosthetic heart valves, to an implantation site in a minimally invasive and percutaneous manner that satisfies the constraints associated with heart valve implantation (e.g., traversing the aortic arch).